Process in the heating of metal billets and an arrangement for carrying out the process



14, 1967 P. o. LoFs'rRdM PROCESS IN THE HEATING OF METAL BILLETS AND ANARRANGEMENT FOR CARRYING OUT THE PROCESS Filed Oct. 18, 1963 INVENTOR.

PER ORVAFK LFs'rRbm HTTOI? NEYS United States Patent PROCESS IN THEHEATING 0F METAL BILLETS AND AN ARRANGEMENT FOR CARRYING OUT TEE PROCESSPer Orvar Ltifstriim, Bromma, Sweden, asslgnor to Svenska MetallverkensUgns Aktiebolag Vasteras, Sweden, a joint-stock company limited FiledOct. 18, 1963, Ser. No. 317,263 Claims priority, application Sweden,Oct. 20, 1962, 11,279/ 62 2 Claims. (Cl. 148134) The present inventionrelates to a process in the heating of metal billets in a heatingfurnace with mechanical transport of the billets through the furnace.

Heating of metal 'billets for subsequent deformation by rolling,pressing or forging, takes place as a rule at temperatures between tento twenty and two to three hundred degrees centrigrade below the meltingpoint of the metal or metallic alloy to be heated.

During heating, the billets undergo certain inner transformation inaddition to which chemical reactions take place on their surfaces. Thespeed of these surface reactions depends partly on the atmospheresurrounding the billets in the furnace and partly on the temperature atthe surface of the material and the time that the material is at thetemperature in question. In the great majority of cases, the surfacereactions involve an undesirable loss of material or a change in thecomposition of the outer layer of the material, which effects, invarious ways, it has been attempted to limit.

In the heat treatment range, excellent results have been obtained by theuse ofshielding gas atmospheres adapted to the nature of the material inorder to limit or eliminate the undesirable surface reactions. However,normal heat treatment usually takes place at lower temperatures and insmaller furnace units than is the case in heating. In high productivelarge heating furnace units therefore, use of shielding gas in theheating furnace has not been undertaken to any great extent, to acertain degree because of technical reasons but primarily for reasons ofeconomy. This, however, does not exclude the possibility of such ameasure gaining increased significance as a means of preventing sufacereaction in heating furnaces as well, especially during the latter partof the heating period until the final temperature has been reached, asthe speed of the surface reaction in furnaces not supplied withshielding gas rises exponentially with the temperature.

The present invention does not assume the use of shielding gas. Itrelates to a process by which, despite the presence of free or boundoxygen in the furnace atmosphere, a considerable reduction of thesurface reaction can be attained compared to what can be obtained withcorresponding manpower in known types of furnace. In addition, theprocess has been developed with a view to its use preferably for steeland steel alloys.

With knowledge of the reaction speed at different temperatures for thematerial to be heated, the process involves dividing the heating into atleast two successive temperature stages, the duration of the differentstages being adjusted in such a way that the surface reactions arelimited as far as possible with regard to the demands placed upon theheated material concerning the necessary uniformity of temperature forthe subsequent deformation.

When heating, for example steel billets or steel alloys, it may be anadvantage to raise the temperature in the first temperature stage toabout 750 C., i.e., somewhat above the transformation point for thematerial in question. At the said temperatures, the speed of the sur-3,304,210 Patented Feb. 14, 1967 face reactions is still comparativelylow, the surface reaction thus being less powerful if transformation inthe whole billet takes place at a lower furnace temperature in the firststage and at a higher temperature in a subsequent stage.

Heating in the second and the possible subsequent temperature stages,takes place at a higher temperature and the transport at a higher speedthan in the stage immediately preceding in order, While retainingthorough through-heating, to limit the surface reactions by making theduration of the stage in question as short as possible.

For heating the billets to temperatures suitable for varioushot-deformation processes, use is made partly of batch furnaces, e.g.,chamber furnaces, carriage-furnaces and pit-furnaces, partly of more orless pronounced continuous feeding furnaces, e.g.,push-through-furnaces, furnaces with rotating hearths, walking beamfurnaces and in certain cases roller-hearth furnaces. The presentinvention relates only to the use of continuous furnaces.

In continuous furnaces of the kind mentioned above, division of thefurnace into different temperature stages can be made by dividin thefurnace space, from the receiving end to the discharge end, into more orless sharply defined zones, the temperature stages coinciding with thesefurnace zones.

The greater the surface area of the billet that is exposed to convectionand radiation, the more quickly heating takes place. It is therefore ofgreat importance that the billets be separate from each other duringtransport.

In the conventional pusher furnace, it has not been possible to satisfythis requirement in that part of the furnace where the billets arepushed forward lying close to each other. In certain embodiments thispart extends throughout the length of the furnace, which means that thespeed at which the billets are advanced is not changed when theyapproach the final temperature. In other embodiments the billets aremechanically pushed forward into a part of the furnace and thereaftermanually rolled, using crow bars, with a certain distance between them,through the final heating Zone to a discharge aperture arrangedfrontally or in the side wall of the furnace. In this method ofprocedure, the above mentioned conditions for effective and speedyheating exist at least in the distance that the billets are rolled. Inthat the rolling speed can be varied, the surface reactions can also belower than for a push-through furnace with the push-through distanceextending throughout its length. The arrangement according to theinvention, however, relates to mechanical transport throughout theentire furnace. The push-through furnace also has certain disadvantagesin that it cannot be completely emptied without considerable manualwork.

Furances with rotating hearths, at least so called ringfurnaces, olferthe possibility of dividing the furnace into Zones corresponding to thetemperature staged stated above. During transport from the receivingaperture to the discharge aperture the billets are more or less separatefrom each other. Transport from the receiving to the discharge aperturesis completely mechanical. The furnace has, moreover, the advantage thatit can be easily emptied if so desired, completely or partially, using.the mechanical means, installed for normal transport of the billets.However, owing to the basic construction of the furnace, it is notpossible to vary the transport speed during passage of the billetsthrough the furnace.

The invention will be further explained below with reference to theattached drawing in which a walking beam furnace is diagrammaticallyillustrated, and in connection with this, further characteristics willbe set forth.

FIGURE 1 shows a longitudinal section of a walking beam furnaceaccording to the invention.

FIGURE 2 shows a modification of the walking beam arrangement accordingto FIGURE 1, likewise in longitudinal section.

FIGURE 3 shows an example of how a frontal discharge chute with adischarge aperture can be arranged.

The furnace shown in FIGURE 1 consists principally of two furnacechambers, 1 for preheating and 2 for final heating. The hearth in thepreheating part consists of one or more parallel movable walking beams3-, and longi tudinal fixed beams situated between them. The number ofparallel beams is determined by the billet-length of the material to beheated in the furnace. In the final heating part 2, the hearth is alsoconstructed as a walking beam system 4, suitably with the same number ofbeams as in the preheating part.

Heating of the furnace takes place in the case chosen by way of example,by oil burners or gas burners or combination burners mounted as sideburners 8 in the preheating part and as gable burners 9 in the finalheating part. The fumes from all burners are led away from the furnacethrough the fume outlet 17. On lighting the oven, and whenoperation ofthe roller mechanism is interrupted, the fume outlet 16 is used for thefinal heating zone and the outlet 17 for the preheating zone.

The beams rest on carrier wheels which are mounted on bell-crank levers11. The bell-crank levers are in turn mounted on hearing pedestals 12standing on concrete bases. By means of hydraulic lift cylinders 14, onefor each walking beam in the beam system in each of the preheating andfinal heating parts respectively, which cylinders are connected to thelevers by pull rods, the movable beams can be raised and lowered in aknown manner. In both beam systems, the movable beams can be movedforwards and backwards in a purely horizontal direction by means ofhydraulic carrier cylinder 13, during which movements the movable beamsroll on the carrier wheels 10. The extreme positions for the raising andlowering movement as well as the backward and forward movement areadjustable so as to be adapted in the most suitable manner to thedimensions of the billets for which the furnace has been constructed.

The time interval between two successive beam cycles, raisingmovingforward--loweringmoving backwards, can also be varied within widelimits. The desired distance between the billets can herewith be simplyadjusted. The position of rest is where the movable beams are in theretracted and lowered position. To seal the beam system against airpenetrating from the beam machinery space 8 under the furnace and forcollecting oxide scales and/or slag dropping from the material, thereare water seals 15, assembled with cleansable oxide throats and slagchutes.

The billets are moved into the furnace through the receiving aperture 5,either by the movable walking beams which possibly extend outside theaperture, as shown in FIGURE 1, or by frontal insertion means, or fromthe side, e.g., on a roller conveyor. The billets are advanced on thebeam system in the preheating zone in steps through the zone so that onexit from this zone they will be automatically moved to the beam systemin the final heating zone and finally delivered from the walking beamsto a discharge toller conveyor 7 and leave the furnace through thedischarge aperture 6 in one of the longitudinal sides of the furnace asis evident from FIGURE 1. In certain cases, with regard to the placingof the furnace in relation to the rolling mill and transport pathbetween the furnace and mill, it can be more advantageous to havefrontal discharge from the furnace. FIGURE 3 shows an example of how adischarge chute 7a and discharge aperture 6a can be arranged in such acase.

Both the walking beam systems can be arranged at the same horizontallevel, i.e., that in adjusted end position for raising and lowering theyare at the same level, as is evident from FIGURE 1. In this case, thebeam systems are not driven completely independently of each other.Synchronization is therewith carried out in such a way that when themovable beam system in the preheating zone executes a forward feedingcycle the movable beam system in the final heating zone executes thesame cycle. After the former beam system has reached rest position, thesynchronization is stopped and the latter beam system can execute adesired number of forward feeding cycles while the beam system in thepreheating zone remains at rest.

In FIGURE 2 an alternative embodiment is shown where both the beamsystems are at different levels and are separated, wherefore transfer ofbillets from the first movable beam system to the second is carried outby means of a short chute, on which the billets, owing to the force ofgravity, slide from the one system to the other. In this case, both beamsystems can be driven independently of each other.

By adjusting the length of the forward movements (stroke length) and thetime interval between the forward movement cycles of the different beamsystems according to the nature of the material of the billets to beheated, the arrangement described presents an excellent and fiexiblemeans of carrying out the process according to the invention.

Having now described the invention, what I claim as new and desire tosecure by Letters Patent is:

1. A method of heating steel billets to a desired high temperature in anoxygen-containing atmosphere comprising passing the billets through apreheating zone to heat the billets uniformly to a moderate temperaturebelow which no substantial surface reaction occurs, immediatelytransferring the billets to a final heating zone, and passing thebillets through said final heating zone rapidly to further heat thebillets uniformly to the desired high temperature in the shortestpossible time so that surface reactions are minimized.

2. Apparatus for heating steel billets to a desired high temperaturecomprising a moderate-temperature preheating chamber open tooxygen-containing atmosphere, walking beam conveyor means for advancingindividual billets through said preheating chamber, a high-temperaturefinal heating chamber open to oxygen-containing atmosphere, walking beamconveyor means for advancing the billets through said final heatingchamber, means for transferring the billets directly from the conveyormeans in the preheating chamber to the conveyor means in the finalheating chamber, means for driving the conveyor means in the finalheating chamber at a faster advancing speed than the conveyor means inthe preheating chamber, and means to proportion the advancing speeds ofthe two conveyor means to reduce the duration of passage of each billetthrough the final heating chamber to the shortest time needed forthrough-heating of the billet to the desired high temperature.

References Cited by the Examiner UNITED STATES PATENTS 2,126,534 8/1938Cope 148-13 2,723,927 11/1955 Tour 148-16.?

DAVID L. RECK, Primary Examiner.

R. O. DEAN, Assistant Examiner.

1. A METHOD OF HEATING STEEL BILLETS TO A DESIRED HIGH TEMPERATURE IN ANOXYGEN-CONTAINING ATMOSPHERE COMPRISING PASSING THE BILLETS THROUGH APREHEATING ZONE TO HEAT THE BILLETS UNIFORMLY TO A MODERATE TEMPERATUREBELOW WHICH NO SUBSTANTIAL SURFACE REACTION OCCURS, IMMEDIATELYTRANSFERRING THE BILLETS TO A FINAL HEATING ZONE, AND PASSING THEBILLETS THROUGH SAID FINAL HEATING ZONE RAPIDLY TO FURTHER HEAT THEBILLETS UNIFORMLY TO THE DESIRED HIGH TEMPERATURE IN THE SHORTESTPOSSIBLE TIME SO THAT SURFACE REACTIONS ARE MINIMIZED.